It has long been known that the life of vehicle tires is prolonged when they are pressurized to desired levels which depend upon the type of tire involved, and that use of such tires will be more trouble free when the proper pressure level is maintained. Discounting methods of achieving desired pressure levels in tires used in automotive assembly lines, there are generally two methods employed in controlling the pressure level within a tire.
One such method is substantially wholly manual. It involves the placing of a pressure gauge in fluid communication with the interior of the tire, generally through the valve stem, and obtaining an indication of the pressure level within the tire. Pressure is then released or added as required either by bleeding excess pressure out of the tire or opening a valve connected to a source of gas under pressure to pass pressurized gas to the interior of the tire. At points in the process, it is necessary to halt gas flow to or from the tire and obtain a pressure reading to determine whether the pressure level desired has been achieved. Not infrequently, the several steps of this process must be repeated a number of times and at the conclusion of an inflation cycle, it may be necessary to bleed off excess pressure since the tire was overpressurized during inflation. The converse may occur during a deflation cycle as well where too much pressure is bled off.
Attempts have been made to automate this process as far as inflation is concerned. In the usual case, the pressurized gas line from a source of gas under pressure is provided with an adjustable pressure regulator and then connected to the interior of the tire, usually by the tire valve stem. A desired pressure level is set on the adjustable pressure regulator and gas will flow from the source to the pressure regulator, be regulated down to the desired pressure set thereon and then flow into the tire until equilibrium is achieved.
While the ultimate result of such system, namely, the achieving of a desired pressure level in the tire, is satisfactorily obtained, such systems have not achieved wide acceptance because of the slowness of operation thereof. In particular, because the pressure of the gas flowing out of the pressure regulator is equal to the desired pressure level to be achieved in the tire, as the desired pressure level in the tire is being reached, the pressure differential required to cause gas flow into the tire becomes progressively smaller. Thus, the flow rate of gas is constantly being reduced and becomes a mere trickel as the desired pressure level is approached. Such systems require so much time to inflate a tire to the desired pressure level that the manual method mentioned previously is employed in the vast majority of cases simply because it is more rapid even though more prone to under or over inflation errors because of the human element involved.
Furthermore, where such systems are employed where a considerable range of tire pressures are to be achieved, additional difficulties attend their use. Specifically, under and/or over inflation errors are not uncommon and difficulty is experienced in accurately achieving the pressure regulator from one pressure to another. This difficulty can be overcome by calibrating the system each time a pressure change is to be made, but recalibration is time consuming thereby further delaying an inflation process.